I already RP having to sleep, but not eating and drinking. One problem I see with hypothermia is racial resistance. Not all races in Skyrim would suffer the cold equally;
So? Makes more reason to choose one race over the other, and have some actual impact over that. If you want the resistance, pick a race that does that and suffer what you miss from the others. More choice having a consequence.
Nords already have a strong resistance to cold, but what about the cold-blooded Argonian? Would Khajiit have roughly the same resistance as Nords due to their fur?
How about this wrt hypothermia:
* Nords gain benefit from their builtin frost resistance in general, but still suffer from the multipliers (see below).
* Argonian lack builtin frost resistance, but don't suffer the "wet multiplier". Makes sense?
* Khajiit lack builtin frost resistance, but don't suffer the "wind multiplier". Makes sense?
You "collect hypothermia points" by current magical means, and in extreme cold (in snowy areas?). Clothes, fur, and hide armor have different insulation values to protect against these natural elements, that gain additional weight by "wet multiplier" that drains off when you get to dry land. Metal armor doesn't have any heat insulation, but they also don't gain this additional weight. This "wet multiplier" increases slowly by rain, and instantly to max (say 4?) if you decide to go for a swim.
The same goes for wind, except it only affects "hypothermia collection speed", as a multiplier (say, 2?). So assume you're well insulated and decide to go for a swim in cold windy weather. If you're gathering 3 points per second for being in a cold environment, that could increase to 3*4 = 12 points per second while in the water (you don't get wind chill factor in water, but water is generally worse), and it continues to climb at 3*2 = 6 points per second outside the water, which will reduce slowly as you dry up. Standing near a fire will speed up the recovery rate considerably. Same with simply going inside.
From what I've heard, consoles already have variable movement speed from their anologue controls. Why not connect current hypothermia speed to your maximum speeds (variable)? This is negated of course if you're using a horse (means I'll suffer

). We could have warning levels on:
1-30% - light hypothermia (-20% in movement speed)
31-60% - moderate hypothermia (-40% in movement speed and regeneration rates)
61-80% - severe hypothermia (-60% in movement speed and regeneration rates)
81-90% - extreme hypothermia (-80% in movement speed and regeneration rates)
91-100% - fatal hypothermia (overencumbered speed, -90% regeneration rates, freeze to death at 100% - could happen, but highly unlikely).
So if you play with this DLC/MOD active, you still have a choice - do you play like a fool taking a swim without preparing for it, or do you choose to take the penalties? It's supposed to make some impact for your choices, not make the game unplayable. It's main purpose is to make you think about your own role playing and your actions, and add adequate penalties if you choose to ignore them. Values above are figurative, it all have to play out nicely and be well balanced. I think FONV did it brilliantly.
Edit: If wind isn't simulated and only exists as a weather effect, then Khajiit could have higher tolerance to sleep requirements and reduced penalties for it, given their slightly nocturnal abilities in general.